Fuse tube construction



" Aug. 27, 193 I R. J.- BRbNlKOWSKl 3,102,173

FUSE TUBE CONSTRUCTION "Filed June 29. 1960 I 2 sheets-sheet 1 IN VEN TOR.

FAD Mama J: BRON/KOd/JK/ Aug. 27, 1963 R. J. BRONIKOWSKI FUS TUBE CONSTRUCTION 2 Sheets-Shee t 2 F iled June 29,- 1960- IN V EN TOR. Re /WM? J 5/?0N/KOMSK/ gl T 3,102,178 FUSE TUBE QQNSTRUCTEON r Raymond J. Bronikowski, South Milwaukee, Wis, assignor to McGraw-Edison Company, Milwaukee, WIS. a corporation of Delaware Filed June 29, 1960, Ser. No. 39,604 8 Claims. (til. 260-120) This invention relates, generally, to electrical circuit interrupt ng means and has particular relation to a fuse construction in which recoil during high current interruptions is substantially reduced without affecting the low current clearingability of the fuse. V I

In interrupting high fault current conditions on an electric line, present day expulsion type fuse tubes rely on gases evolved from the fuse tube to extinguish the electrical arc resulting from the rupture of the fuse link. Since these gases are generated in a relatively confined space at a high rate they are under high pressure and this pressure aids in extinguishing the arc aswell as expelling ionized gases from the confines of the fuse tube. tube and subsequent venting of gases, over a short period of time, leads to the development of high recoil forces on the-fuse tube assembly. During individual cases of current interruption the recoil forces may reach such a value that portions of the interrupting device or the mounting bracket may be permanently deformed or otherwise damaged. Even if the recoil forces do not permanently deform portions of the interrupting device they may, in the case of a drop out fuse cutout, cause premature drop out of the fuse tube thereby burning the contact members. Excessive pressures within the fuse tube may also result in rupturing the fuse tube itself.

As distribution systems increase in size, the interrupting duty requirements of the interrupting devices also increase. Pressure build up in the fuse tube and recoil or thrust forces due to expulsion of gases from the'fuse tube increase at least in proportion to the increase in current.

To reduce maximum pressure, prior art devices have frequently relied on increasing the inside bore of the fuse tube. This expedient served to increase the area within the tube and therefore to reduce the pressure of a given volume. of evolved gas. However, the pressure decrease was far from dramatic since, as the crosssectional area of the fuse tube bore, increased as the square of the diameter, the surface of the gas evolving fiber exposed to the are increased linearly with the diameter of the tube.

In increasing the inside bore of the fuse tube prior art constructions experienced additional difiiculties in that the fuse tube did not consistently clear the circuit at the first current zero but carried over for additional half cycles of arcing. The additional force impulses caused by this prolonged arcing generally served to nullify the modest thrust reduction obtained from using a larger bore.

Another serious problem encountered in enlarging the fuse tube bore was that low current clearing ability was adversely affected by the enlarged bore. Lowcurrent clearing depends on the physical dimensions and properties of the link protector tube and fuse tube bore. Hence prior art devices in utilizing construction having a larger fuse tube bore ran into the difficulty that under certain transient conditions the link protector tube was alone unable to extinguish the arc and the fuse tube bore was 'too large to allow sufficient pressure build up to extinguish the are at the particular current level. As a result the low current clearing ability of the fuse tube was seriously undermined by enlarging the bore to reduce thrust at high current values.

3,162,178 Patented Aug. 27, 1963 ice It is academic that a lowcurrent arc that persists for several cycles can be extremely damaging to a given piece of equipment, as for example, afault on the secondary of a transformer which if not cleared quickly, by the fuse cutout in series with the primary winding, will result in severe overheating and possible damage to the windings of the transformer.

I have found that by shielding portions of the gas evolving liner in a fuse tube from the arc that material This build up of pressure within the fuse v reductions may be made in the internal gas pressure of the fuse tube without resorting to increasing the bore of the fuse tube and consequently impairing the low current clearing abilities of the fuse tube.

It is therefore an object of the invention to provide a fuse tube construction that will experience lesser pressure build up within the fuse tube during current interrupting operations.

Another object of this invention 15 to provide a fuse tube construction that will experience low thrustforces during high current interruption.

Another object of this invention is to provide a fuse tube construction that will experience low thurst forcesduring high current interruption while maintaining the low current interrupting capabilities of the fuse tube.

A further object of this invention is to provide a fuse construction that will shorten the arc during high current interruption and which will shield a, portion of the gas evolvingtubular liner from the arc during high current interruption.

A still. further object of this invention is to provide a fuse construction having a lesser amount of gas evolving material in direct contact with the electrical arc without substantially altering the interrupting characteristics of the fuse tube.

Other objects and advantages of my invention will be apparent from the following description of the preferred embodiments of the invention taken in connection with the accompanying drawings in which:

7 FIGURE 1 is a view in elevation of a fuse cutout in which the invention may be utilized;

FIGURE 2 is a view in elevation of a longitudinal cross-section of a fuse tube embodying my invention;

FIGURE 3 is a view in elevation of a longitudinal cross-section of a fuse tube embodying a modified form FIGURE 4 is a view in elevation of a longitudinal cross-section of a fuse tube embodying another modified form of the invention.

Referring now to FIGURE 1 of the invention, 9 desig-.

nates a fuse cutout having a fuse tube or cartridge 10 which may have a liner of bone fibre and an outer, insulating covering of phenolic, glass reinforced-thermosetting resin or other similar material.

The fuse cartridge 10 is supported between upper and lower fuse supports 9' and 9 respectively. Upper and lower spaced apart contacts 14, 16 respectively are affixed to fuse tube 10 and in electrical engagement with stationary contacts (not shown) on the fuse supports 9 and 9". A' fuse link 18' extends throughout the fuse tube iii and has the lower end thereof held tightly as by means 11. It can thusly be seen that the fuse tube 10 and fuse link 18 serve to electrically bridge the space between upper and lower contacts 14, 16.

Referring now to FIG. 2 the upper end of the fuse tube ltl has screw threads ltla on the outer periphery thereof which engage internal screw threads 12 on ferrule portion 13 of upper terminal contact member 14; Perrule portion 13 of member 14'has a longitudinally extending bore 13a therethrough which is in axial alignment with and in communication with the interior of the fuse tube 10. The bore 13:: of ferrule portion 13 is of a larger diameter than bore 14a of member 14 so that the ferrule member 13 may embrace for the ends o f'the fuse tubes.

threaded extremities of the fuse tubes 30, 40 bottom re-- .with respect too-ne another.

the upper extremities of the fuse tube s Means for mounting a pull ring assembly 15, and contact arm 17 may be integral with or otherwiseafi ixed to terminal contact member 14. Lower contact terminal member 16 is aflixed to the lower extremity of the fuse tube 10 and may be in embracing relation thereto.

A fuse link 18 having a ferrule adapter extension 19 and a link protector tube 18 therearound extendswithin bore 14a, bore 13a and fuse tube 10' and forms a current path; between upper contact member 14 and lower contact member 16. 'The upper end of ferrule adapter 19 may be formed to a button head 19' so that it rests upon the upper margin of terminal member 14. While the ferrule adapter 19, which may be of brass, is shown extending into the upper area of fuse tube 10 it is to be understood that it may extend for a relatively great distance into fuse tube 10 or that it may extend for only a portion of the length of terminal member 14 or that it may not extend at all into'fuse tube 10 but this is not shown. Closure means 21 engages screw threads 22 on the upper end of terminal member 14 and serves to close one end of the fuse tube.

A gas evolving fiber liner extends from the top of the fuse tube 10 throughout most of the length of the tube. A portion of the liner 20 is cut away intermediate the ends of the fusetube and conductive sleeve 23 replaces the so cutaway liner. The sleeve 23 is preferably of metal but may be of any other non-insulating, conductive material and may include insulating materials which will carbonize.

While the conductive sleeve 23 is shown in FIGURE 2' as replacing a portion of the gas evolving liner 20 it might equally well be cemented to or otherwise affixed to a portion of the liner 2ft thereby alleviating the necessity of cutting away a' portion of the liner 20 or alleviating the necessity of providing a split (two piece) liner originally.

In FIGURE 3 .a slightly modified construction is shown wherein conducting sleeve member 32 joins fuse tubes and 40 having gas evolving liners 31 and 33 respectively, together. As before, the construction of FIGURE 3 includes an upper terminal member 14,v lower contact terminal member 16, closure member 21, and fuse link 18.

The conductive sleeve member 32 has a bore 32w which communicates with the interior of fuse tubes 30 and 40 ends of fuse tubes 30, 40 respectively. Internal shoulder portions 44, 45 of the sleeve member 32 serve as stops Normally when the spectively on shoulder portions 44, 45 of the sleeve member 32 the'sleeveand fuse tubes 30, 40'will be properly aflixed to one another and otherwise properly positioned It can be seen that by using the conductive sleeve connector 32 that a substantial amount of gasevolving. fiber is eliminated as compared to the heretofore described fuse tube constructions. Note also, that even though the amount of gas evolving fibre has been reduced that the confined area surrounding the fus link has been virtually undiminished.

7 radial shoulder portions 57 adjacent extensions 53, 5'4 and each serves respectively as a stop for the lower end of fuse tube 50 and the upper end of fuse tube 60.

In FIGURE 4 the sleeve 52 serves to shield a portion 'of the In both the modifications of FIGS. 3 and 4 electrical insulating material may be utilized to insulate theexterior portions of the sleeve member although this is not shown. similar expedients could be utilized in place of the screw connections to join the sleeve member andfuse tubes together.

The operation of all three embodiments issubstantially similar and will now be explained.

During low overcurrents of up to approximately 40 0 amperes several cycles of current are generally required before the rupturable fuse link melts. Upon rupture of the fuse link 18 some amount of gas is generated by the link protector tube 18 as a result of the rise in temperature within the link protector tube due to arcing between ruptured ends of the fuse link. The gas so generated quickly permeates the confines of the protector tube and serves to extinguish the arc. The fuse link flip out lever 27 (FIG. 1) also serves to aid in extinction of the are by separating the ruptured endsof the fuse link. Hence the arc is extinguished and the equipment to be protected is effectively isolated from the line. Note that subsequentto fuse link extraction the fuse, tube will drop out thusly providing a large air gap.

In the case of fault currents. in excess of 400 amps. the same sequence as in interruption of low currents will occur except that e gas generated bythe protector tube 18' will be insufficient to extinguish the are. As

more and more gases are evolved pressure builds up within the link protector tube and it bursts and/or is expelled from the fuse tube. The arc is then exposed to portions of the gas evolving liner and gases are evolved at a rapid rate thusly increasing the pressure within the fuse tube. Venting at one end of the fuse tube then takes place propelling the ruptured fuse link ends apart as well as expelling ionized gases and relieving pressure within the tube. As current approaches zero the diameter of the arc diminishes and disappears as the zero point is reached.

The incorporation of a conductive sleeve serves to effectively limit the amount of gases generated in the tube and thereby reduces the thrust force and subsequent cutout recoil caused by gases under pressure being expelled from one end of the fuse tube. Note that while there is a reduced area of liner capable of evolving gases that the area available for gas expansion is relatively unaffected. Since control of the gases being evolved is effected through theuse of a non-insulating (conductive) liner and not by an increase in the bore of the fuse tube the low current interrupting capabilities of the fuse tube remain intact. More particularly fault currents in the intermediate range (400-800 amps.) sufficient to cause rupture of the fuse link protector but not ordinarily sufficient to cause a substantial volume if gas to be evolved from the gas evolving liner will, in the instant device, cause a sufficient volume of gas to be evolved to extinguish the arc since there is no increase in the diameter of the fuse tube bore.

It is particularly to be noted that on high current faults A subsequent to rupture of the fuse link that the length of the resultant arc increases. The are originally exists between the ruptured ends of the fuse link but as the arc increases in length it is transferred from one end of the fuse link to the metal sleeve member. A second arc in seriesnwith the first arc is then created between the lower end of the metal sleeve member and a portion of the fuse leader below the sleeve. It can thuslybe seen that whereas one elongated arc was present in prior same electrical conditions. Hence since a portion of 7 It should also be understood that cement or bers and in fact best results are achieved when" the sleeve is removed 1-3 inches from the open end of the fuse tube. This floating 'condition of the conductive or even in close proximity to either of the electrodes, the low current clearing capabilities of the tube will be detriinentally afiected. I

It may thusly be seen that my invention results in substantially lesser arc lengths, better cooling, lesser volumes of evolved gases and therefore a much diminished thrust force. All this is achieved without detrimentally effecting the high or low current clearing ability of a fuse tube.

For example in utilizing my invention to interrupt current of 6000 amps, I have been able to reduce recoil forces from 900 pounds thrust to 650 pounds thrust, a reduction of 28% without detracting from the low current clearing ability of the fuse tube.

While three particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications can be made therefrom without departing from the spirit of the invention and, therefore, it is intended that the appended claims cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a circuit interrupting device the combination of, a gas evolving expulsion fuse tube having a rupturable fuse link therewithin, upper and lowerterrninal means associated with said fuse tube and in electrical contact with said fuselink, closure means for one end'of said fuse tube, whereby a recoil forceis exerted upon said fuse tube as a result of the gas expelled from the open other end thereof when said fuse link ruptures, conductive sleeve means within said fuse tube and surrounding I said fuse link, said conductive sleeve means being electrically isolated from said upper and lower terminal means, whereby subsequent to rupture of said fuse link said conductive sleeve means functions to shorten the length of the resulting arc and to decrease the area of said fuse tube available to evolve gases thereby decreasing said recoil force on said fuse tube.

2. In a circuit interrupting device, a gas evolving expulsion fuse tube having a rupturable fuse link there within, closure means for one end of said fuse tube, whereby gases expelled from the open other end of said fuse tube incident to rupture of said fuse link result in areactive force thereon, and upper and lower terminal contact means associated with said fuse tube and in electrical contact with said fuse link, in combination with, electrically conductive sleeve means within a portion of said fuse tube in surrounding relation to a portion of said fuse link, said electrically conductive sleeve means being electrically separated from said upper and lower contact means and having a bore which is substantially equal in size to the bore of said fuse tube, said sleeve means decreasing the area of said fuse tube available to generate gases and shortening the are formed upon rupture of said fuse link, whereby the energy in said are and said reactive force are reduced.

3. In an expulsion fuse cutout of the drop out type the combination offirst and second gas evolving fuse tube means in axial alignment with one another, electrically conductive sleeve means interposed between said first and ing an internal diameter no greater than that of said sleeve is important since if the sleeve'isin contact with, p

fuse tube means and having an extended circumferential portion and an inner shoulder portion on eachend, said shoulder portions of said conductive sleeve means serving as a stop for each of said fuse tubes and said extended portions embracing the outer periphery of each of said fuse tubes, upper and lower terminal contact means associated with said first and second fuse tubes respectively, a rupturable fuse link within said fuse tubes and said conductive sleeve means and electrically bridging said upper and lower terminal contact means and having a rupturable portion spaced axially of said fuse tube means from said conduotivesleeve means, closure means for said first tube means, whereby a recoil force is exerted on said fuse cutout as a result of the gases expelled from said second fuse tube means when said fuse link ruptures, said conductive sleeve means decreasing the area of said expulsion type fuse tube available to generate gas and shortening the are formed upon rupture of said fuse link and reducing said recoil force.

4. In a drop out type fusecutout the combinaton of first and second gas evolving fuse tubes in axial alignment with one another, conductive sleeve means interposed between said first and second fuse tubes and together therewith forming an expulsion type fuse tube, said conductive sleeve means having an internal diameter no greater than that of said fuse tubes and having on both ends an outer circumferential shoulder portion and an inner portion that extends beyond said shoulder portion in an axial direction, said inner portions of said conductive sleeve means being receivable within the bore sleeve means, and closure means for said first fuse tube,-

whereby gas expelled from said second fuse tube incident to rupture of said fuse link results in a reactive force on said expulsion type; fuse tube, said sleeve means reducing the area of said expulsion type fuse tube available to evolve gas and shortening the length of the are formed upon rupture of said fuse link, whereby the are energy and said reactive force are decreased.

5. In a fuse cutout, in combination, an expulsion fuse tube, gas evolving material on the internal periphery of said fuse tube, terminals on the ends of said fuse tube, a fuse link within said fuse tube connected to said terminals and having a rupturable portion, closure means for one end of said fuse tube, whereby the gas expelled from the open other end cf said fuse tube upon rupture of said fuse link results in a recoil force on said fuse tube, an insulating protector tube surrounding said rupturable portion within said fuse tube, fuse link tensioning means for extracting a severed portion of said fuse link from said fuse tube after rupture of said rupturable portion, an electrically conductive sleeve having an inner diameter no greater than that of said fuse tube surrounding said fuse link within said fuse tube and being spaced axially of said fuse tube from said rupturable portion, said conductive sleeve being normally isolated electrically from said terminals and decreasing the area of said fuse tube available to evolve gas and shortening the are formed upon rupture of said rupturable portion, whereby the energy of said arc is reduced and said recoil force is decreased.

6. In acircuit interrupting device, the combination of gas evolving expulsion fuse tubular means having a fuse link therewithin having a rupturable portion, closure means for one end of said tubular means, whereby the 7 gas expelled from the open other end of (said tubular means upon rupture of said fuse link results in a recoil force on said tubular means, upper and lower terminal means associated with said tubular means and in electrical contact with the ends of said fuse link, conductive means within said tubular means' surrounding said fuse link for shielding a portion of said tubular means from the arccreated upon rupture of said fuse link, said conductive means being normally spaced axially of said tubular nieansfromsaid nupturable portion and electrical:

1y isolated from said upper and lower terminal contacts,

said conductive means shortening said are and decreasing the area of said expulsion fuse tubular means available to evolve gas, whereby said recoil force is reduced.

. 7. In a circuit interrupting device the combination of a gas evolving expulsion fuse tube having a rupturable fuse link therewithin, terminal means on, said fuse tube electrically connected to said fuse link, closure means for one end of said fuse tube, whereby gases expelled from the open other end of said fuse tube incident to rupture of said fuse link result in arecoil force on said fuse tube,

electrically conductive means surrounding a portion of said fuse link for shielding a portion of said gas evolving fuse tube from the arc resulting between ruptured ends evolving expulsion fuse tubular means having a fuse link therewithin, said fuse link having a'ruptur'a ble portion intermediate the ends thereof, spaced apart terminal means affixed to said tubular means and electrically con nected to said ends of said fuse link, closure means for one "end of said tubular means, whereby gas expelled from the'open other end of said tubular means incident to rupture of said fuse link results in a recoil force on said tubular means, electrically conductive sleeve means having an internal diameter no greater than that of said tubular means CllSPOSfid'Vl/llhlll said tubular means and surrounding said fuse link and being spaced axially of said tubular means from said ruptur'able portion, said electrieally conductive sleeve means being normally electrically isolated from said spaced apartterminal means,

said electrically conductive sleeve. means decreasing the area of said tubular means available to evolve gases and shortening the are created upon rupture of saidfuse link and a substantial portion of the voltage of said are occurring between said conductive means and a severed portion of said fuse link adjacent said rupturable portion,

thereby facilitating arc interruption and decreasing said recoil force.

References Cited in the file of this patent UNITED STATES PATENTS Link Dec. 22, 1959 

8. IN A DROP OUT FUSE CUTOUT THE COMBINATION OF, GAS EVOLVING EXPULSION FUSE TUBULAR MEANS HAVING A FUSE LINK THEREWITHIN, SAID FUSE LINK HAVING A RUPTURABLE PORTION INTERMEDIATE THE ENDS THEREOF, SPACED APART TERMINAL MEANS AFFIXED TO SAID TUBULAR MEANS AND ELECTRICALLY CONNECTED TO SAID ENDS OF SAID FUSE LINK, CLOSURE MEANS FOR ONE END OF SAID TUBULAR MEANS, WHEREBY GAS EXPELLED FROM THE OPEN OTHER END OF SAID TUBULAR MEANS INCIDENT TO RUPTURE OF SAID FUSE LINK RESULTS IN A RECOIL FORCE ON SAID TUBULAR MEANS, ELECTRICALLY CONDUCTIVE SLEEVE MEANS HAVING AN INTERNAL DIAMETER NO GREATER THAN THAT OF SAID TUBULAR MEANS DISPOSED WITHIN SAID TUBULAR MEANS AND SURROUNDING SAID FUSE LINK AND BEING SPACED AXIALLY OF SAID TUBULAR MEANS FROM SAID RUPTURABLE PORTION, SAID ELEC- 